Summary of significant accounting policies - Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Summary of significant accounting policies
Cash	$ 0.3		$ 0.3		$ 0.3
Guaranteed investment certificates	0.3		0.3		$ 0.3
Software development costs capitalized	1.2		$ 1.2
Amortization period			5 years
Amortization expense	$ 0.1	$ 0.0	$ 0.2	$ 0.0